Here is the recipe I used to bake:
1 cup oats
120g brown sugar
1/4 tsp salt
1/4 tsp baking soda
Filling: blueberry 125 g, sugar 70g, 40ml lemon juice, 2 tsp cornstarch.
First, make filling:
Boil blueberries, sugar and lemon juice in a pot. Simmer till tender about 10 mins. Add in cornstarch, stir till thickened about 1 min. Remove from heat and cool.
In a large bowl, mix oats, flour, brown sugar, salt, and baking soda. Cut in butter and form crumbs.
Spread 1/2 crumbs into pan as base. Then spread blueberry filling. The rest crumbs as top.
Preheat oven to 180 degree C. Bake for around 40mins until lightly golden.
Cut it into squares after cooled.